The invention relates to a method and apparatus for producing a parison by means of a pressing process in a parison mold of a press-blow glass forming machine.
In the case of a known apparatus of this type (U.S. Pat. No. 4,336,050 A) the loading orifice is located at the top in a block mold which is not longitudinally divided. A longitudinally-divided parison mold middle piece is disposed between the block mold and the neck mold. The neck mold comprises a longitudinally-divided neck tool and a guide ring, which is not longitudinally-divided and is held in a radial groove of the neck tool, for the pressing plunger. The end operating position of the pressing plunger is defined by virtue of the fact that an upper annular surface of a pressing plunger holder moves into position against an annular counter surface of the guide ring. Owing to the axial play, which increases as the wear increases, between the guide ring and the closed neck tool the end operating position changes in an undesired manner. The axial outer sealing edge of the neck is obviously formed by the opposite radial end face of the guide ring. This leads to undesired sharp-edged glass seams, which are pressed into the mold gaps at the transition from the radially extending, axially outer sealing edge to the adjacent radially inner and radially outer neck contour. These glass seams also impair the sealing effect between the neck and its closure device.
With respect to the prior art, FIGS. 1 and 2 of U.S. Pat. No. 4,662,928 A disclose a forming tool of a blow-blow machine known per se for producing champagne bottles. It comprises a longitudinally-divided parison mold and a longitudinally-divided neck tool. An axially moveable plunger lies in its axial end operating position against the closed neck tool. The plunger forms a small, radially inner part of the axially outer sealing edge of the neck of the champagne bottle. The remaining part of the sealing edge is formed by the neck tool. An annular glass seam is pressed between these two sealing edge parts into the parting line between the plunger and the neck tool (FIGS. 2 and 3A). Moreover, opposite perpendicular glass seams, which originate from the juncture plane of the neck tool, extend as far as into the sealing edge. These glass seams must be subsequently removed in a costly procedure by xe2x80x9cfire polishingxe2x80x9d (FIG. 3B). In order to avoid these disadvantages U.S. Pat. No. 4,662,928A proposes to allow the entire sealing edge to be formed by a guide ring which is not divided and which is held in the neck tool (FIGS. 4 to 6). However, this then causes similar disadvantages to those experienced in U.S. Pat. No. 4,336,050A.
In the case of apparatus known per se (FIG. 1 or EP 0 327 240 A1) the end operating position of the pressing plunger is determined exclusively by the deforming resistance of the molten glass when the cavity is completely filled with glass and the parison has been completely pressed. Thus, the end operating position of the pressing plunger depends upon the respective mass of the gob and/or of the respective volume of the cavity. The pressing plunger comprises on its foot a slightly conical, almost cylindrical guide section. The slight conical shape is intended to facilitate the subsequent removal of the pressing plunger from the parison. On a final part of the path of the pressing plunger as far as into its end operating position the guide section is received into a guide ring, which is not longitudinally divided, and as a result is centered in the radial direction and guided. Owing to the slight conical shape of the guide section a radial gap, whose width depends upon the respective end operating position of the pressing plunger, remains between the guide section and the guide ring. During the pressing process it is possible in certain operating situations for the glass mass to penetrate into this gap in an undesired manner. The guide ring is held radially outside in a holding groove of the neck tool. The guide ring comprises on its end facing the cavity a forming ring for forming the axially outer sealing edge of the neck of the parison.
It is known per se from U.S. Pat. No. 4,411,681 A to raise a plunger first into its end operating position in which a ring of the plunger lies against an undivided guide ring of a neck mold (FIGS. 1 to 3). A glass gob then falls into a filling orifice of a mold cavity of a longitudinally- and transversely-divided parison mold and onto the tip of the plunger. A blow head is introduced from the top into the filling orifice (FIG. 2) and blows the glass gob firmly into the parison mold and the neck mold and around the plunger, wherein a space is existing between the blow head and the glass (FIG. 3). The plunger is subsequently lowered into a middle position (FIG. 4). Compressed air is introduced through the neck and preliminarily blows the parison until it also contacts the blow head. Finally, the finished parison is removed from the parison mold (FIG. 5). This combined process of settle and preliminarily blowing the parison whilst using the plunger requires an expensive construction and a comparatively long cycle. Moreover, it is disadvantageous that a sealing edge of the neck of the parison is formed by means of the guide ring.
It is known per se from U.S. Pat. No. 4,411,681 A to raise a plunger first into its end operating position in which a ring of the plunger lies against an undivided guide ring of a neck mold (FIGS. 1 to 3). A glass gob then falls into a filling orifice of a mold cavity of a longitudinally- and transversely-divided parison mold and onto the tip of the plunger. A blow head is introduced from the top into the filling orifice (FIG. 2) and blows the glass gob firmly into the parison mold and the neck mold and around the plunger, wherein a space is existing between the blow head and the glass (FIG. 3). The plunger is subsequently lowered into a middle position (FIG. 4). Compressed air is introduced through the neck and preliminarily blows the parison until it also contacts the blow head. Finally, the finished parison is removed from the parison mold (FIG. 5). This combined process of settle and preliminarily blowing the parison whilst using the plunger requires an expensive construction and a comparatively long cycle. Moreover, it is disadvantageous that a sealing edge of the neck of the parison is formed by means of the guide ring.
It is known per se from DE 32 32 288 C1 to introduce the glass gob into a block mold cavity. The volume of the block mold cavity is first enlarged by an additional volume. This can occur by moving a piston downwards in a base cavity of the block mold. The additional volume is nullified again by virtue of the upwards movement of the piston until the parison has been formed.
Apparatus for adjusting the mass of the glass gob on a feeder device is known per se from GB 2 178 421 A.
The object of the invention is to improve the manner in which the neck of the parison is formed.
This object is achieved with respect to the method by virtue of a method for producing a parison in a parison mold, wherein the parison has a neck, a base and an axially outer sealing edge of the neck. The parison mold has a cavity and a neck mold, the neck mold having a through passage and a neck tool which forms the neck of the parison, and wherein the neck tool has a stop surface. The method includes the following steps: (a) introducing a gob of molten glass into the cavity of the parison mold; (b) pressing a pressing plunger into the gob through the through passage until the pressing plunger reaches an end operating position defined by the stop surface to preliminarily press the parison; and (c) simultaneously with or following step (b), exerting pressure on the base of the parison with a pressing element, which defines part of the cavity, until the cavity is completely filled with the molten glass and the parison is finished-pressed, wherein the axially outer sealing edge of the neck is completely formed by the pressing plunger.
Owing to the fact that the pressing plunger moves into position against the neck tool, the pressing plunger, in an extremely precise manner, always reaches the same end operating position irrespective of the mass of the glass gob and the volume of the cavity in the parison mold. This creates uniform inner contours of the necks of the parisons. Furthermore, because the entire axially outer sealing edge of the neck is no longer formed by the guide ring but rather by the pressing plunger itself, the slightly conical guide section can be formed in a more conical shape at the foot of the pressing plunger in a favorable manner. As a consequence, the pressing plunger can be removed easier from the finish-pressed parison and damage to the neck inner surface of the parison is prevented. The parison is pressed in two stages. In the first stage the parison is pre-pressed by the pressing plunger until the pressing plunger reaches its end operating position and in the second stage the parison is finish-pressed by the pressing element. The result is a parison with an ideally pressed-out, undamaged neck and also the glass is distributed in an extremely favorable manner. The invention is particularly suitable for use in the so-called I.S. (Individual Section) press-blow glass forming machines.
Additional features of the invention include contacting the gob with the pressing element within the cavity opposite to the pressing plunger upon the step of pressing the pressing plunger through the through passage and into the gob of molten glass; and moving the pressing element in a direction out of the cavity, where the moving is done by the gob acting on said pressing element. These features hold the pressing element in contact with the glass for a comparatively long period of time.
Additional features are provided where the parison mold includes longitudinally-divided parison mold halves having a loading orifice formed in a base of the parison mold halves, and wherein the above method further includes the steps of: introducing the gob of molten glass into the cavity through the loading orifice; and closing the loading orifice with the pressing element. Here, the loading orifice can be designed in a funnel-like manner in order to improve and facilitate the manner in which the glass gob can be introduced without interference into the cavity. In most cases this negates the requirement for a separate loading funnel. Such a loading funnel would otherwise need to be moved as a separate element over the loading orifice for loading purposes and be removed once the loading is complete. This would mean higher structural and operational costs.
It is not possible in practice to avoid fluctuations in the mass of the glass gob. The features of another embodiment of the invention render it possible in a rapid and reliable manner to influence the manner in which the desired optimum gob mass is maintained. Such features include determining a maximum penetration depth of the pressing element into the cavity by sensing the movement of the pressing element relative to the parison mold; and controlling the mass of the gob of molten glass introduced into the cavity by sensing the movement of the pressing element relative to the parison mold.
The object mentioned above is achieved with respect to the apparatus by virtue of an apparatus for producing a parison from a gob of molten glass wherein the parison has a neck, a base, and an axially outer sealing edge. The apparatus includes:
a parison mold having a cavity, a loading orifice through which the molten gob is received into the cavity, and a neck mold having a longitudinally divided neck tool for forming the neck of the parison, the neck mold having a through passage;
a pressing plunger movable through the through passage for pressing into the glass gob in the cavity, the pressing plunger being movable to an end operating position against the neck mold wherein the pressing plunger lies against the neck tool, the pressing plunger being configured to completely form the axially outer sealing edge, the pressing plunger being removable from the parison after the parison has been formed; and
a pressing element movable relative to the parison mold and which defines a part of the cavity, the pressing element capable of exerting pressure on the base of the parison in the cavity until the cavity is filled with the molten glass and the parison is finished-pressed, including the formation of the axially outer sealing edge. Essentially the same advantages as mentioned above in connection with the method are achieved.
The parison mold of the apparatus can further include longitudinally-divided parison mold halves, the loading orifice being formed in a base of the parison mold halves, and the pressing element is movable into the cavity through the loading orifice and is capable of closing the loading orifice. The loading orifice can in preference be formed in the shape of a funnel in order to facilitate and improve the manner in which the glass gob is introduced into the cavity.
In another embodiment, the parison mold comprises a non longitudinally-divided block mold which has a locking ring that lies adjacent to the neck tool. The pressing element is displaceably mounted in a lower base orifice of the block mold, and the neck tool in the upwards direction is adjacent to the loading orifice of the block mold. These features are of particular advantage when producing wide-neck ware. The closed parison mold can be held together in a particularly convenient manner. It is necessary to hold the parison mold together in order to prevent it opening during the pressing procedure when the pressing forces attempt to open the individual parts of the parison mold. If the parison mold were to open, gaps would occur in the mold into which the glass mass could be pressed in an undesired manner. A longitudinally-divided parison mold middle piece can also be disposed between the block mold and the neck tool according to DE 32 32 288 C1. In this manner it is also possible using a block mold to produce narrow-neck ware.
In another embodiment, the apparatus can further include a shaft adjacent to a foot of the pressing plunger. The shaft has an annular end face and is wider than the pressing plunger. The apparatus also includes a forming ring for forming the complete axially outer sealing edge of the neck, the forming ring being formed in the annular end face. According to these features, the axially outer sealing edge of the neck is no longer formed by a guide ring in the neck tool or by the neck tool, but rather is formed completely by an element of the pressing plunger. This increases the precision in the manner in which the neck is formed. Furthermore, the neck tool can include a stop surface engageable with the end face of the shaft to define the end operating position of the pressing plunger. Here, the end operating position can be achieved structurally in a particularly convenient manner.
By virtue of the features of another embodiment, the pressing plunger can be guided in a precise radial manner in the final path section, which is of particular importance for forming the parison, in the radial direction on a cylindrical shaft surface. In this embodiment, the apparatus includes a cylindrical shaft adjacent to a foot of the pressing plunger, and a centering ring fixed relative to the parison mold. The cylindrical shaft is received on a last part of the path of the pressing plunger as far as its end operating position in the centering ring so as to be guided and centered in the radial direction through the centering ring. Where the centering ring is undivided longitudinally and held radially outwards in a holding groove of the neck tool, the centering ring is also held in a reliable manner in the neck tool when the neck tool is open. The neck tool is only opened during operation for the purpose of discharging the hollow glass object which is finish-formed in the finish-forming station.